1. Field of the Invention
The present invention relates to a spring assembly for level controlling support of a wagon body on a running gear of a vehicle, in particular of a railway vehicle, comprising a spring device and an actuator device. The spring device takes up a first installation space, while the actuator device takes up a second installation space. The spring device and the actuator device are connected to each other in a direction of action in a kinematically serial arrangement, wherein the actuator device is designed for at least partially compensating for a change in length of the spring device in the direction of action by a displacement at an actuator component in the direction of action. The present invention also relates to a vehicle having such a level-controlling spring assembly.
2. Description of the Related Art
In railway vehicles (but also in other vehicles) the wagon body is usually resiliently mounted with respect to the wheel units (e.g. single wheels, pairs of wheels or wheelsets) by way of one or a plurality of spring stages. Differing degrees of deflection of the springs in these spring stages occur over time depending on the loading of the railway vehicle. With a purely passive system or without appropriate countermeasures this leads, by way of example, to the passengers having to negotiate a more or less high step upon boarding or exiting when the railway vehicle stops at platforms with a certain, constructionally predetermined platform level above the top edges of the rail (which define the reference level). Boarding and/or exiting can potentially be made considerably more difficult hereby, especially for passengers with physical limitations. A further cause, in addition to varying loading, of such an undesirable step when boarding and/or exiting lies, moreover, in the wear occurring over time on the wheels of the wheel units.
Different approaches are taken in known vehicles with active systems to counteract this problem. In conventional vehicles with a secondary suspension comprising pneumatic springs the level of the wagon body can, by way of example, be easily controlled by way of appropriate adjustment of the pneumatic pressure in the pneumatic springs. However, such pneumatic spring systems have the drawback that, owing to the limited operating pressure (typically at a maximum pressure of about 7 bar), as a rule they take up a relatively large installation space in order to be able to apply the required supporting forces.
An active spring system is also known from DE 103 60 518 B4 in which an actuator of a hydropneumatic actuator device is arranged between the wagon body and a bogie frame to be kinematically parallel to a passive spring (by way of example a conventional helical spring) of the secondary suspension. This actuator can be used to actively adjust the level of the wagon body by exerting (parallel to the supporting force of the passive spring) an appropriate actuating force between the wagon body and the bogie frame.
While the desired level control can be achieved when stopping at platforms using such an active system, there is the problem that level control via the actuator must, as a rule, firstly be switched off during travel in order to achieve the desired spring effect (otherwise a very complex, highly dynamic controller would be necessary for the actuator). Secondly, a malfunction of the actuator, by way of example a blocking, can lead to significant stiffening of the secondary suspension which is highly undesirable with regard to both the derailment safety system and travelling comfort.
Finally, a generic active spring system is known from DE 102 36 245 A1 in which an actuator of an actuator device is arranged between the wagon body and a bogie frame to be above and in a kinematically serial arrangement with respect to a passive spring (e.g. a conventional helical spring) of the secondary suspension. The actuator arranged coaxially to the spring can be used to actively adjust the level of the wagon body in that it compensates a change in the length of the spring (as results by way of example from a change in the loading of the vehicle) by its own appropriate change in length (i.e. a displacement at one of its components).
The desired level control when stopping at platforms as well as during travel can be achieved using this active system. However, there is the problem that the kinematically serial arrangement of spring and actuator results in a large construction, in particular in the height direction of the vehicle, which, with an installation space predetermined for the secondary suspension (as a rule within comparatively narrow limits), can only be integrated in the vehicle with considerable effort without a loss in relation to the vehicle safety and comfort properties (hence with sufficiently low stiffness).
The object underlying the present invention is therefore to provide a spring assembly or a vehicle of the type mentioned in the introduction which does not exhibit said drawbacks, or at least to a lesser extent, and in particular easily and reliably allows integration of level control in a vehicle without significant reductions in the travelling safety and travelling comfort for the passengers.